JP2010541436A - Method and configuration for event-driven adaptive cell detection activity level in discontinuous reception - Google Patents

Abstract

In a cellular communication network, user equipment can adjust the strength (or measurement activity) of identifying a new neighboring cell based on a comparison between the quality of the identified neighboring cell and the quality of the reference cell. Downlink received signal levels (eg, CPICH Ec / No or / and SCH Ec / No) from appropriately selected neighboring cells (cells belonging to the active set or candidate set) are referenced by a certain threshold (eg, Serving) If not below the cell, reduce this strength. On the other hand, if the downlink received signal level from the selected neighboring cell (eg, CPICH Ec / No or / and SCH Ec / No) is below the reference cell by a certain threshold, the UE Identify new cells with high intensity.
[Selection] Figure 2

Description

  The present invention relates to a method and configuration in a mobile communication system, and more particularly to neighbor cell identification activity.

  In wideband code division multiple access (WCDMA) networks and next-generation universal terrestrial radio access networks (E-UTRAN), mobility determination with cell reselection and handover is performed by user equipment (UE) search for new cells And heavily dependent on the downlink measurements of the identified cells. For this reason, the UE needs to measure and track a certain number of best cells in terms of downlink measurement quality in order to ensure good UE mobility.

  In active mode WCDMA, the UE needs to detect (or identify) a new co-frequency cell in at least 800 milliseconds. In addition, the UE measures the downlink quality (ie CPICH measurement) of at least 8 cells (1 serving cell and 7 neighbors) while meeting the minimum performance requirements specified in TS 25.133 [1]. Must be able to report.

  In E-UTRAN, it is likely that similar measurement performance requirements will be defined following those used in WCDMA [2].

Movement scenario There are basically two types of mobile scenario.
Idle mode mobility: Cell reselection connected mode mobility: Handover

  Cell reselection is an autonomous function of the UE that mainly does not go through the serving cell. However, the operation of the UE in this mobility scenario can be controlled to some extent according to some system parameters and performance specifications that are broadcast.

  On the other hand, handover is completely controlled by network and performance specifications using explicit UE specific commands.

  As will be described in detail in connection with the description of the problem, the mobility determination is made mainly based on the same kind of downlink measurement values in both the idle mode and the connected mode.

WCDMA and E-UTRAN are both frequency reuse-1 systems. This means that the geographically closest neighboring cells operate on the same carrier frequency. Since an operator may use multiple frequency layers within the same service area, any idle mode and connected mode mobility of WCDMA and E-UTRAN can be broadly classified into the following three main categories.
Mobility within the same frequency (idle mode and connected mode): The UE moves between cells belonging to the same carrier frequency. This is the most important mobility scenario because of the low cost of delay. In addition, the operator has at least one carrier that is free to use efficiently.
Mobility between different frequencies (idle mode and connected mode): A UE moves between cells belonging to different carrier frequencies but having the same access technology. This movement scenario can be regarded as the next most important scenario.
Mobility between different radio access technologies (idle mode and connected mode): The UE moves between cells belonging to different access technologies such as between WCDMA and GSM or vice versa.

Aspects of UE measurements related to mobility To ensure good mobility performance in WCDMA or E-UTRAN, the UE performs two main tasks:
Identification of new cells, i.e. identification in complete synchronization with unknown cells.
Regularly perform downlink measurements on several plots or reference signal channels from a certain minimum number of identification cells (eg CPICH Ec / No and RSCP in WCDMA [3], RSRP and RSRQ in E-UTRAN) Report measurements.

In order to ensure good mobile performance, the requirements for the measurement task are defined. In WCDMA included in the specification range, the following contents are defined so that the UE surely satisfies at least the above-described requirements. Some of the important requirements for active mode include: [1]
Unknown cell identification delay for a given reception level of the corresponding synchronization and CPICH signal. The upper limit of the delay is a maximum of 800 milliseconds in the case of the same frequency cell in the continuous reception mode (that is, not using DRX).
The required minimum number of identification cells (8 cells including 1 serving cell and 7 neighbors) for which the UE reports CPICH measurements with specified measurement absolute and relative accuracy.
A measurement time of 200 milliseconds in which the specified measurement accuracy of at least 8 cells is met.

  Similar requirements are defined for E-UTRAN.

Cell Identification Processing at the UE In order to report this requirement number of identification cell downlink measurements to the network, the UE periodically searches for new cells that are better than the current and old cells (in other words, identifies )There is a need. Terms such as cell detection, cell search, and cell identification have the same meaning and indicate the UE's ability to fully synchronize to unknown cells (ie, detect cell timing, cell identifier, etc.). The cell to be identified may or may not be on the neighbor cell list provided from the network to the UE.

  In order to meet such standardized minimum requirements and due to changing radio conditions, the UE must periodically identify and measure neighboring cells. Such scheduling of measurement processing is not standardized and is unique when the UE is mounted. In order to limit hardware costs and prevent running out of battery, the UE typically collects measurement samples of different types of measurements at certain regular intervals.

  In idle mode, the UE mainly performs measurements during paging occasions (ie, at wake up at the end of the DRX cycle). Therefore, the measurement sampling rate in the idle mode is considerably lower than that in the connection mode. For this reason, the measurement performance in the idle mode is much lower than that obtained in the connected mode.

Effect of Discontinuous Reception (DRX) in Active Mode on Cell Identification WCDMA Release 7 defines a new function called discontinuous reception (DRX) in connected mode (more specifically, CELL_DCH state) [5]. Accordingly, since the UE wakes up only at a fixed time according to the DRX cycle, the UE can save battery while being connected. In Release 7, the longest DRX cycle is 40 milliseconds.

  In general, the DRX function mainly collects measurement samples at the time of wakeup or at least less frequently than in the case of continuous reception. Therefore, the measurement requirements are relaxed in Release 7 DRX mode [1]. Given DRX of 40 milliseconds and UE activity level of 5%, identification of the same frequency cell in DRX (Release 7) may take up to 6 seconds in the worst case [1]. Therefore, the active mode DRX generally may have some adverse effects on mobility performance, particularly cell identification performance. On the other hand, however, the 6 second delay is still acceptable for packet data services that have a higher tolerance for delay. From this it can be seen that only a maximum of 10% of the users are affected. This is because an active set update, in which in most cases single or multiple cells are replaced with newly identified cells, takes longer than 6 seconds. However, better performance is desirable for real-time services.

  The introduction of new WCDMA services and future enhancements will likely require more DRX options. However, current requirements based on the latest technology schemes are expected to be inadequate to meet the goal of mobility performance (ie, the call dropping rate is reduced).

  In E-UTRAN, active mode DRX allows the network to use a DRX cycle of up to 2.56 seconds. For this reason, when the current method is used, the cell identification time may be unnecessarily prolonged.

Problems with traditional solutions
Cell Identification in DRX Scenario In DRX mode, when the UE identifies a new cell only during the active time, the target cell is inferior in terms of reception quality (eg CPICH Ec / No and / or SCH Ec / No). If so, the delay is obviously longer.

  On the other hand, when always identifying in the DRX mode, the UE provides the same cell identification performance as that obtained in the continuous reception mode, and the UE battery is consumed. For this reason, even if it has a DRX function, there is no advantage.

  Low measurement performance and a significant increase in cell identification delay results in active set update delays. This delay in turn causes a handover decision delay at the base station whose handover execution depends on UE measurement reports. Thus, in active mode, performance degradation associated with such measurements must be minimized to prevent unnecessary cold dropping.

  Several modern solutions have been proposed to minimize cell identification performance degradation when using DRX in active mode. Some of these will be described below.

Cell identification with high SCH and CPICH reception levels In the currently agreed solution, the minimum reception level of the cell's synchronization channel (SCH) and common pilot channel (CPICH) is significantly higher (eg 3dB higher than in non-DRX case ) In some cases, UEs in DRX state make measurements to identify cells. Since the strength of the cell is relatively high, cell identification is relatively fast on average.

The adjustment network of cell identification delay based on absolute threshold provides the UE with an absolute threshold and measurement activity factor at the CPICH Ec / Io or CPICH RSCP level. The latter parameter is used to increase or decrease measurement activity (eg, cell identification time, measurement time) depending on the CPICH Ec / Io and / or CPICH RSCP reception level of the strongest monitor cell in the active set.

  If the received CPICH Ec / Io and / or CPICH RSCP from the serving cell is above the transmitted threshold, the UE needs to identify a new co-frequency cell according to the measured activity factor. As a result, the cell identification delay usually increases as a result of the transmitted activity factor. On the other hand, if the condition is not met, i.e. the quality of the serving cell is low (below the Ec / No and / or RSCP threshold), the UE will delay as much as specified for continuous reception (i.e. 800 mm). Identify the new cell with a worst case delay of seconds [1].

  In this case, there is one difficulty, for example, the UE has to measure frequently even if there is no need to measure such that there are relatively good cells in the active set. Thus, in practice, the UE has to wake up during the DRX length inactive time. As a result, the battery of the UE is consumed, and the advantage of the DRX operation cannot be obtained.

Switching to continuous mode (non-DRX) in the cell boundary region In the WCDMA specification [5], the active mode network prompts the UE to switch between DRX mode and non-DRX mode with low level signaling. it can. For this reason, as a possible solution for speeding up the measurement process, there is a method of returning to the non-DRX mode (or a very short DRX cycle) when the UE enters the cell boundary region. The network can determine whether the UE is within the cell boundary region by comparing the downlink channel quality (eg, CPICH level) reported by the UE with a certain threshold. Usually 25-35% of users operate within the cell boundary region. Thus, the UE can barely maintain the DRX state by an average of about 65-75% at that time. This method is not desirable from the viewpoint of UE battery saving because the UE cannot fully utilize DRX.

  The main limitation of the prior art solutions described above is that such solutions do not take into account the relative performance differences between the serving cell and the target cell / neighboring cell. This difference is an important factor in mobility performance, particularly in the frequency of new cell identification.

  An object of the present invention is to provide a method that takes into account the relative performance difference between a serving cell and a target cell / adjacent cell.

  In general, the downlink received signal level (eg, CPICH Ec / No or / and SCH Ec / No) from appropriately selected neighboring cells (cells belonging to the active set or candidate set) is a serving cell by a certain threshold. If not, the UE identifies the new cell with a relatively low strength (or measurement activity). On the other hand, if the downlink received signal level from the selected neighboring cell (eg, CPICH Ec / No or / and SCH Ec / No) is below the serving cell by a certain threshold, the UE Identify with higher intensity.

  According to one aspect of the invention, the downlink received signal level (eg, CPICH Ec / No or / and SCH Ec / No) from at least the Nth strongest neighbor cell (cell belonging to the active set or candidate set) is If it is not below the serving cell by a certain threshold, the UE identifies the new cell with a relatively low strength (or measurement activity). On the other hand, the downlink received signal level (for example, CPICH Ec / No or / and SCH Ec / No) from at least the Nth strongest neighbor cell (target cell, or cell belonging to the active set or candidate set) is constant. If it is below the serving cell by the threshold, the UE identifies the new cell with higher strength.

  According to another aspect, the downlink received signal level (eg, CPICH Ec / No or / and SCH Ec / No) from the weakest neighbor cell of the active set or candidate set is below the serving cell by a certain threshold. If not, the UE identifies the new cell with a relatively low strength (or measurement activity). On the other hand, if the downlink received signal level (eg, CPICH Ec / No or / and SCH Ec / No) from the weakest cell belonging to the active set or candidate set is below the serving cell by a certain threshold, the UE Identifies new cells with higher intensity.

  The serving cell may not be the strongest cell. Thus, in another series of aspects, cell identification or detection performance is determined by the difference in reception level (eg, CPICH Ec / No or / and SCH Ec / No) between the strongest cell and the Nth strongest target cell or neighboring cell. Determined.

1 shows a cellular communication network according to the present invention. 3 is a flowchart illustrating a first method according to an aspect of the present invention.

  FIG. 1 schematically shows a cellular communication network operating in accordance with the present invention.

  The service area of the network is divided into cells 10, 12, 14, 16, 18, 20, 22 and the like. Since the user apparatus (UE) 24 is located in the cell 12 and communicates with the base station (eNode B) 26 in the cell, this cell corresponds to the serving cell of the UE. As is well known, the UE must measure signals received from other cells in order to identify potential neighboring cells. Although the present invention is described herein primarily with reference to LTE (Long Term Evolution) (E-UTRAN) networks, it should be understood that the present invention is applicable to many other networks.

  FIG. 2 is a flow chart illustrating a first method according to the present invention.

  In step 50, the UE detects a threshold used in the method. In step 52, the UE compares the quality measurements obtained for the reference cell with the quality measurements obtained for a certain number of other already identified cells. If step 54 determines that the comparison criteria are met, processing proceeds to step 56 to increase the level of cell detection activity or intensity. On the other hand, if it is determined in step 54 that the comparison criteria are not met, the process proceeds to step 58 to reduce the level of cell detection activity or intensity.

  According to one embodiment of the invention, the cell detection activity or strength of a new cell is determined by the UE after comparing the quality level of the identified cell with the quality level of the serving cell. Thus, in one embodiment, the network uses at least one relative threshold that the UE can use to compare cells with respect to downlink reception levels such as common pilot channel (CPICH) Ec / No and synchronization channel (SCH) Ec / No. Send. The threshold value may be a fixed value standardized in the specification.

  Furthermore, the network can transmit the parameter “N”, ie the number of strongest cells that need to compare the received level with the received level of the reference cell. In the preferred embodiment, this reference cell is a serving cell. In another embodiment, the comparison is performed on the best cell. As with the threshold, this number (N) may be a standardized value.

  The new cell detection activity differs depending on whether the difference in measurement quality between the serving cell and the target cell is larger or smaller than the relative threshold.

  If cell detection activity or strength is low, the UE will often detect a new cell during the discontinuous reception (DRX) wake-up time or for a much longer time than required for continuous reception. Will do.

  On the other hand, if the cell detection strength is high, the UE continuously identifies cells or the DRX cycle becomes very short. As a result, cell detection performance (that is, cell detection delay) similar to that obtained in the case of continuous reception is obtained.

  As described further below, there may be intermediate cell detection intensities depending on the number of relative threshold levels used.

Criteria for defining relative thresholds (cell comparison criteria)
The relative threshold determines which measurement quality should be used for the UE to perform cell comparison. In other words, the comparison criterion is determined by the relative threshold. For example, the threshold can be represented by one or more of the following parameters.
Adjacent cell measurement level: WCDMA desired wave received power (RSCP) and / or Ec / No, E-UTRAN reference symbol received power (RSRP) and / or reference symbol received quality (RSRQ).
SCH reception level: For example, SCH signal-to-noise interference ratio (SINR), SCH Ec / No, BER, received signal strength, and the like.
Received signal level of known pilot symbol or reference symbol Cell identification delay history of existing cells of active set or candidate set

  In WCDMA, a suitable relative threshold for determining cell detection strength is expressed as a relative CPICH Ec / No and / or SCH Ec / No level. This is because cell identification requirements are specified for a given SCH and CPICH reception level.

  In addition, it is conceivable that the comparison is performed based on the above-described single or plural determination criteria.

  Further, the relative threshold may be a single level or a plurality of levels (M). In the former method, the network transmits only one threshold for each criterion. The result is two cell detection activity levels (standard or high and low). In the latter method, the network can send multiple relative thresholds per criterion, so that the UE has to acquire multiple cell detection activity levels (ie M + 1 for M thresholds). Don't be.

  For simplicity, a single level is preferred for the threshold, and in most cases a single level is appropriate.

  The network may also specify how often the UE must compare cells based on a relative threshold (eg, a comparison period). For this specification, a parameter may be transmitted, or for example, it may be specified by the number of frames, the number of DRX cycles, or a fixed period.

The signaling mechanism of the N cells to be compared with the relative threshold value The threshold value and other related parameters (for example, the period of comparing the cells and the number N of cells in the active set or candidate set to be compared) It can be transmitted in a state-of-the-art manner through control (RRC) and higher layer signaling. The threshold may be transmitted to all UEs through a broadcast channel or to a specific UE through a specific control channel of the UE. Furthermore, in the idle mode and the active mode, different threshold values can be used for the same criterion.

  In WCDMA, since there is RRC in the radio network controller (RNC), the RNC controls such threshold signaling. In E-UTRAN, the threshold is transmitted by a base station (or eNode B in E-UTRAN terminology).

The UE new cell detection activity of the reference cell specific target cell for comparison is based on the relative performance difference between the target cell and the reference cell, and can be roughly divided into the following two.
Comparison with serving cell Comparison with best cell

  In the embodiment in which the reference cell is the serving cell, the UE always compares the target cell with the serving cell according to the determination criterion or criteria described in the section regarding the determination criterion for defining the relative threshold. Based on this comparison, the UE decides whether to detect a new cell with high intensity or with low intensity.

  For example, using both pilot signal quality (E-UTRAN RSRQ, or WCDMA CPICH Ec / No) and SCH reception level (eg, E-UTRAN SCH SINR, or WCDMA SCH Ec / No), The detection activity or strength level of the new cell shall be determined. Furthermore, it is assumed that there is only a single level relative threshold, ie α and β, for RSRQ (or CPICH Ec / No) and SCH SINR (or SCH Ec / No), respectively.

Next, one or both of the measured quality differences between the N best cells or the strongest cells (ie for WCDMA SCH Ec / No and / or CPICH Ec / No) and the serving cell S have a corresponding threshold value. If it falls below, the frequency of identification of new cells by the UE becomes low (as a result, the cell identification delay deteriorates and increases). Thereby, the following relationship is established.
IF
(Q _N −Q _S ≦ α) OPERATOR (P _N −P _S ≦ β)
THEN
Identify new cells with lower activity or lower intensity.
ELSE
Identify new cells with higher or normal intensity.
However,
Q = E-UTRAN RSRQ and WCDMA CPICH Ec / No
P = E-UTRAN SCH SINR and WCDMA SCH Ec / No

  In one embodiment, OPERATOR is set to AND for both E-UTRAN and WCDMA. Alternatively, OPERATOR is set to OR in both cases of E-UTRAN and WCDMA.

  In another embodiment, only one of the measurement quality (Q or P) may be used by the UE in the algorithm to determine the measurement activity level of the target cell.

In one embodiment, Q _N and P _N represent each signal level received from the weakest cell of N neighboring best cells of the active set or candidate set. As described above, the value of N can be transmitted to the UE. By changing the value of N, the overall detection activity can be changed. Alternatively, the value of N can be stored in the UE.

In another embodiment, Q _N and P _N similarly represent each signal level received from the weakest cell in the active set or candidate set.

  In embodiments where the reference cell is the best cell, the UE always compares the target cell or neighboring cells with the best cell, but this best cell does not necessarily have to be a serving cell.

  As described above, the UE uses one or more of the criteria described in the section relating to the criteria defining the relative threshold. Based on this comparison, the UE decides whether to detect a new cell with high intensity or with low intensity. However, this method may not provide sufficient information about the target cell (for example, when the strongest cell has no resources).

  For example, using both pilot signal quality (E-UTRAN RSRQ or WCDMA CPICH Ec / No) and SCH reception level (eg E-UTRAN SCH SINR or WCDMA SCH Ec / No) Let us determine the detection activity or strength level of the new cell. Furthermore, it is assumed that there is only a single level relative threshold, ie α and β, for RSRQ (or CPICH Ec / No) and SCH SINR (or SCH Ec / No), respectively.

Next, one or both of the measured quality differences between the N best cells or the strongest cells (ie, for WCDMA SCH Ec / No and / or CPICH Ec / No) and best cell B are the corresponding threshold values. If it is less than the threshold, the frequency of identification of new cells by the UE is reduced (as a result, the cell identification delay is worsened and increased).
IF
(Q _N −Q _B ≦ α) OPERATOR (P _N −P _B ≦ β)
THEN
Identify new cells with lower activity or lower intensity.
ELSE
Identify new cells with higher or normal intensity.
Symbols: Q, P, and OPERATOR have the same meaning as described above.

In one embodiment, Q _K and P _K represent each signal level received from the weakest cell of N adjacent best cells of the active set or candidate set.

In another embodiment, Q _K and P _K similarly represent each signal level received from the weakest cell in the active or candidate set.

Combined Detection of Adaptive Cells Based on Relative Threshold and Measurement Activity Based on Relative Threshold FIG. 3 shows a flowchart illustrating yet another method according to the present invention.

  In step 70, the target cell is identified. In step 72, the quality of the target cell is compared with the quality of the reference cell. Based on the result of this comparison, step 74 can adjust the measurement activity of the target cell.

  Thus, it is possible to adjust the measurement activity or intensity level of the identified target cell based on the relative threshold between the serving / best cell and this target cell.

  It should be noted here that, first, the relative threshold used for cell detection and other parameters need not be the same. Secondly, the concept of the adaptive measurement activity based on the relative threshold according to the present invention and the concept of the adaptive cell detection activity based on the relative threshold can be effective not only when used simultaneously but also independently.

The following advantages are obtained by the present invention.
In DRX mode, the UE searches for new cells at high speed only when necessary, i.e. only if there are relatively weak cells in the active or candidate set.
The network can track all the required number of target cells without degrading measurement performance.
The UE can save battery as much as possible while making the best use of DRX.
A reasonably good cell change or handover performance can be maintained.

Reference [1] 3GPP TS 25.133, “Requirements for Radio Resource Management (FDD)”
[2] 3GPP TS 36.801, “Next Generation Universal Terrestrial Radio Access (E-UTRA): Measurement Requirements”
[3] 3GPP TS 25.215, “Physical Layer Measurement Method (FDD)”
[4] 3GPP TS 36.214, “Next Generation Universal Terrestrial Radio Access (E-UTRA): Physical Layer Measurement Method”
[5] 3GPP TS 25.214, “Physical Layer Procedure (FDD)”
[6] RP-070679, “Extended UE-DRX for FDD”, Nokia, Nokia Siemens Networks, Qualcomm, LG Electronics, Philips, NXP
[7] 3GPP R4-071242, "Measurements during CPC downlink DRX operation", Marvell, RAN4 # 44 conference

Claims (34)

In a user equipment of a cellular communication system, a method for identifying a new neighboring cell, comprising:
Comparing the quality level of the identified cell with the quality level of the serving cell;
Setting a new cell detection activity based on the comparison;
Having a method. Said step of comparing the quality level of the identified cell with the quality level of the serving cell;
Determining whether a quality of a downlink received signal from a selected cell of the identified cell is below the serving cell by a threshold value;
If the quality of the downlink received signal from the selected cell of the identified cell is not below the serving cell by a threshold, the new cell detection activity is set to a first strength and the identified cell If the quality of the downlink received signal from the selected cell is lower than the serving cell by a threshold, the new cell detection activity is set to the second strength, and the second strength is set to the first strength. The method of claim 1, wherein the strength is higher than   The method according to claim 1 or 2, wherein the quality level is evaluated based on a desired wave received power (RSCP).   The method according to claim 1 or 2, wherein the quality level is evaluated based on CPICH Ec / No.   The method according to claim 1 or 2, wherein the quality level is evaluated based on reference symbol received power (RSRP).   The method according to claim 1 or 2, wherein the quality level is evaluated based on reference symbol received quality (RSRQ).   The method according to claim 1 or 2, wherein the quality level is evaluated based on a SCH signal to noise interference ratio (SINR).   The method according to claim 1 or 2, wherein the quality level is evaluated based on SCH Ec / No.   The method according to claim 1 or 2, wherein the quality level is evaluated based on a bit error rate.   The method according to claim 1 or 2, wherein the quality level is evaluated based on received signal strength.   A method according to any preceding claim, wherein the quality level is evaluated based on a combination of measurements.   The method of claim 2, wherein the threshold is received by the user equipment during signal transmission from the cellular communication system.   The method of claim 2, wherein the threshold is stored by the user device.   The step of comparing the quality level of the identified cell with the quality level of the serving cell includes comparing the quality level of one cell of the identified cells with the quality level of the serving cell, The method according to any of the preceding claims, wherein the cell is of the lowest quality among a predetermined number of cells of the identified cells.   The method of claim 14, wherein the predetermined number is received by the user equipment during signal transmission from the cellular communication system.   The method of claim 14, wherein the predetermined number is stored by the user device. A user equipment for a cellular communication system method comprising:
Compare the quality level of the identified cell with the quality level of the serving cell,
Based on the comparison, by setting a new cell detection activity,
User equipment configured to identify new neighbor cells. Said step of comparing the quality level of the identified cell with the quality level of the serving cell;
Determining whether the quality of a downlink received signal from a selected cell of the identified cell is below the serving cell by a threshold;
If the quality of the downlink received signal from the selected cell of the identified cell is not below the serving cell by a threshold, the new cell detection activity is set to a first strength and the identified cell If the quality of the downlink received signal from the selected cell is lower than the serving cell by a threshold, the new cell detection activity is set to the second strength, and the second strength is set to the first strength. The user device according to claim 17, wherein the user device is higher than the strength of the user device.   The user apparatus according to claim 17 or 18, wherein the quality level is evaluated based on a desired wave received power (RSCP).   The user equipment according to claim 17 or 18, wherein the quality level is evaluated based on Ec / No.   The user equipment according to claim 17 or 18, wherein the quality level is evaluated based on reference symbol received power (RSRP).   The user equipment according to claim 17 or 18, wherein the quality level is evaluated based on reference symbol reception quality (RSRQ).   The user equipment according to claim 17 or 18, wherein the quality level is evaluated based on a SCH signal-to-noise interference ratio (SINR).   The user equipment according to claim 17 or 18, wherein the quality level is evaluated based on SCH Ec / No.   The user equipment according to claim 17 or 18, wherein the quality level is evaluated based on a bit error rate.   The user equipment according to claim 17 or 18, wherein the quality level is evaluated based on received signal strength.   27. The user equipment according to any one of claims 17 to 26, wherein the quality level is evaluated based on a combination of measured values.   The user equipment according to claim 18, wherein the threshold is received by the user equipment during signal transmission from the cellular communication system.   The user device according to claim 18, wherein the threshold value is stored by the user device.   The step of comparing the quality level of the identified cell with the quality level of the serving cell includes comparing the quality level of one cell of the identified cells with the quality level of the serving cell, The user apparatus according to any one of claims 17 to 29, wherein the user apparatus is a cell having the lowest quality among a predetermined number of cells of the identified cells.   The user apparatus according to claim 30, wherein the predetermined number is received by the user apparatus when a signal is transmitted from the cellular communication system.   The user device according to claim 30, wherein the predetermined number is stored by the user device.   A network node configured to send a threshold to a user equipment for comparison between a quality level of a reference cell and a quality level of an identified cell.   34. The network node according to claim 33, further configured to transmit the number of identified cells to a user equipment for the comparison.